Antal Andrea, Kincses Tamas Z, Nitsche Michael A, Bartfai Orsolya, Paulus Walter
Department of Clinical Neurophysiology, Georg-August University, Göttingen, Germany.
Invest Ophthalmol Vis Sci. 2004 Feb;45(2):702-7. doi: 10.1167/iovs.03-0688.
Transcranial direct current stimulation (tDCS) has been shown to modify the perception threshold of phosphenes elicited by transcranial magnetic stimulation (TMS). The current study was undertaken to examine whether tDCS, when applied over the occipital cortex, is also able to affect visual-evoked potentials (VEPs), which characterize occipital activation in response to visual stimulation, in a polarity-specific way.
For this purpose, VEPs evoked by sinusoidal luminance grating in an on/off mode were recorded before, immediately after, and 10, 20, and 30 minutes after the end of 5, 10, or 15 minutes of anodal or cathodal tDCS of the primary visual cortex.
Significant effects were observed only when low-contrast visual stimuli were applied. Cathodal stimulation decreased, whereas anodal stimulation increased the amplitude of the N70 component. The effect of cathodal stimulation was significant immediately after and 10 minutes after the end of stimulation, if the stimulation duration was sufficiently long (i.e., 10-15 minutes). An increase of N70 amplitude by anodal stimulation was significant only 10 minutes after the end of the 15 minutes tDCS. Cathodal stimulation tended also to affect the amplitude of the P100 component; however, the effect of stimulation was inverse. The amplitude increased immediately after the end of cathodal stimulation. In contrast, anodal stimulation did not affect the P100. The latencies of the N70 and the P100 were not affected by tDCS.
tDCS appears to be a suitable method of inducing reversible excitability changes in a polarity-specific way, not only in the motor but also in the primary visual cortex. The duration of the induced aftereffects depends not only on stimulation duration but also on stimulation polarity. Cathodal stimulation seems to be more effective, in line with previous reports on the motor cortex.
经颅直流电刺激（tDCS）已被证明可改变经颅磁刺激（TMS）诱发的光幻视的感知阈值。本研究旨在探讨当tDCS应用于枕叶皮质时，是否也能够以极性特异性方式影响视觉诱发电位（VEP），VEP是枕叶对视觉刺激反应激活的特征。
为此，在对初级视觉皮质进行5、10或15分钟的阳极或阴极tDCS之前、结束后即刻以及结束后10、20和30分钟，记录以开/关模式呈现的正弦亮度光栅诱发的VEP。
仅在应用低对比度视觉刺激时观察到显著效应。阴极刺激降低，而阳极刺激增加N70成分的波幅。如果刺激持续时间足够长（即10 - 15分钟），阴极刺激的效应在刺激结束后即刻和结束后10分钟时显著。阳极刺激使N70波幅增加仅在15分钟tDCS结束后10分钟时显著。阴极刺激也倾向于影响P100成分的波幅；然而，刺激效应相反。阴极刺激结束后波幅立即增加。相比之下，阳极刺激不影响P100。N70和P100的潜伏期不受tDCS影响。
tDCS似乎是一种不仅在运动皮质而且在初级视觉皮质以极性特异性方式诱导可逆性兴奋性变化的合适方法。诱发的后效应持续时间不仅取决于刺激持续时间，还取决于刺激极性。与先前关于运动皮质的报道一致，阴极刺激似乎更有效。
